SP7662ER-L/TR

SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator September 2012 Rev. 2.1.0 GENERAL DESCRIPTION APPLICATIONS The SP7662 is a synchronous voltage mode PWM step down (buck) regulator capable of a constant output current up to 12 Amps. A wide 5V to 22V single input voltage range allows for single supply operations from industry standard 5V, 12V and 18V power rails. Operations down to 3V are supported with an additional biasing voltage.  Distributed Power Architectures  Point of Load Converters  Power Supply Modules  FPGAs, DSPs and Processors Supplies FEATURES With a 300kHz constant operating frequency and integrated high and low side switch, the SP7662 reduces the overall component count and solution footprint. In addition to a 1% output setpoint accuracy, this device provides high efficiency, low ripple and excellent line and load regulation. An enable function and soft start feature allow for controlled power up sequencing implementation.  12A Continuous Current Built-in current limiting, UVLO, output shortcircuit and over temperature protection insure safe operation under abnormal operating conditions.  Type II & III Compensations Support The SP7662 is offered in a RoHS compliant, lead free 26-pin 7mmx4mm DFN package.  5V-22V Single Input Voltage Rail  3V-22V Input Voltage with 5V Bias  PWM Voltage Mode Control  300kHz Fixed Synchronous Operations  Low RDSON Power Switches  0.8V Min. Output Voltage – 1% Accuracy  Programmable Soft Start  Over Temperature & Short Circuit Protection/Auto-Restart  Current Limiting  RoHS Compliant Lead Free 26-Pin DFN  US Patent #6,922,041 TYPICAL APPLICATION DIAGRAM Fig. 1: SP7662 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 – Fax. +1 510 668-7001 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Input Voltage Range VCC .............................. 4.5V to 5.5V Input Voltage Range VIN .................................. 3V to 22V Junction Temperature Range ....................-40°C to 125°C Thermal Resistance θJC ........................................ 5°C/W Thermal Resistance θJA ...................................... 36°C/W VCC ...................................................................... 7.0V VIN ........................................................................ 25V BST ...................................................................... 30V LX-BST..................................................... -0.3V to 7.0V LX ............................................................... -1V to 30V All other pins ................................... -0.3V to (VCC+0.3)V Storage Temperature .............................. -65°C to 150°C Power Dissipation .....................Internally Limited via OTP Lead Temperature (Soldering, 10 sec).................... 300°C ESD Rating (HBM - Human Body Model) .......................... LX, VINP, PGND................................................... 400V All other pins ....................................................... 2kV ELECTRICAL SPECIFICATIONS Specifications with standard type are for an Operating Junction Temperature of TJ = 25°C only; limits applying over the full Operating Junction Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at T J = 25°C, and are provided for reference purposes only. Unless otherwise indicated, 4.5V < VCC < 5.5V, 3V < VIN < 22V, BST = LX + 5V, UVIN = 3V, CVCC = 1µF, CCOMP = 0.1µF, CSS = 50nF. Parameter Min. Typ. Max. Units VIN Supply Current (No switching) 1.5 3.0 mA VIN Supply Current (Switching) 8 20 mA BST Supply Current (No switching) 0.2 0.4 mA 3 6 mA Conditions Quiescent Current BST Supply Current (switching) • VFB= 0.9V • VFB= 0.9V Protection: UVLO VCC UVLO Start Threshold VCC UVLO Hysteresis 4.00 4.25 4.5 V • 300 mV • 100 200 UVIN Start Threshold 2.30 2.50 2.65 V • UVIN Hysteresis 200 300 400 mV • 1.0 µA • UVIN Input Current UVIN=3.0V Error Amplifier Reference Error Amplifier Reference 0.792 0.800 0.808 V Error Amplifier Reference Over Line 0.784 0.800 0.816 V • 70 150 230 µA • VFB=0.9V, COMP=0.9V -230 -150 -70 µA • VFB=0.9V, COMP=0.9V VFB Input Bias Current 50 200 nA • VFB=0.8V COMP Clamp 3.5 3.8 V COMP Sink Current COMP Source Current COMP Clamp Temp. Coefficient © 2012 Exar Corporation 3.2 -2.0 2X Gain Config., Measure V FB; VCC=5V VFB=0.7V, TA=25°C mV/°C 2/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator Parameter Min. Typ. Max. 5.3 Units Conditions VCC Linear Regulator VCC output Voltage Dropout Voltage • VIN=6 to 22V, ILOAD=0mA to 30mA • VIN=5V, ILOAD=20mA mV • VIN-VOUT=Dropout voltage when VCC regulated drops by 2%, IV CC=30mA 1.20 V • 2.3 V • 4.7 5.0 4.51 4.73 250 500 750 0.80 1.00 1.7 2.0 V Control Loop Ramp Amplitude RAMP Offset Ramp offset Temperature Coefficient -2 GH Minimum Pulse Width 50 Maximum Controllable Duty Ratio Maximum Duty Ratio 92 mV/°C • 180 97 100 % • % • 300 345 KHz 255 Soft-start, Short Circuit, Current Limit and Thermal Protection • SS Charge Current -16 -10 -4 µA • SS Discharge Current 1.0 2.0 3.0 mA • Short Circuit Threshold Voltage 0.2 0.25 0.3 V • Hiccup Timeout • Oscillator Frequency Valid for 20 cycles Fault Present, SS=0.2V 170 220 270 ms Overcurrent Threshold Voltage 54 60 66 mV ISP, ISN Common Mode Range 0 3.6 V 155 °C Guaranteed by design °C Thermal recovery on decreasing temperature Thermal Shutdown Temperature 135 Thermal Hysteresis 145 10 VFB=0.5V Measured ISP - ISN Output Power Stage High Side Switch RDSON Synchronous Low Side Switch RDSON Maximum Output Current © 2012 Exar Corporation 21 25 m VGS=4.5V, IDRAIN=5A, TA=25°C 9 15 m VGS=4.5V, IDRAIN=5A, TA=25°C A 12 3/19 • Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator BLOCK DIAGRAM Fig. 2: SP7662 Block Diagram (Exar’s SP6133 controller based) PIN ASSIGNMENT Fig. 3: SP7662 Pin Assignment © 2012 Exar Corporation 4/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator PIN DESCRIPTION Name Pin Number Description PGND 1-4 GND 5,9,19,20,28 Ground Pin. The control circuitry of the IC and lower power driver are referenced to this pin. Return separately from other ground traces to the (-) terminal of COUT. VFB 6 Feedback Voltage and Short Circuit Detection pin. It is the inverting input of the Error Amplifier and serves as the output voltage feedback point for the Buck Converter. The output voltage is sensed and can be adjusted through an external resistor divider. Whenever VFB drops 0.25V below the positive reference, a short circuit fault is detected and the IC enters hiccup mode. COMP 7 Output of the Error Amplifier. It is internally connected to the inverting input of the PWM comparator. An optimal filter combination is chosen and connected to this pin and either ground or VFB to stabilize the voltage mode loop. SS 8 Soft Start. Connect an external capacitor between SS and GND to set the soft start rate based on the 10μA source current. The SS pin is held low via a 1mA (min) current during all fault conditions. ISN 10 Current sense negative input. Rail-to-rail input for over current detection. ISP 11 Current sense positive input. Rail-to-rail input for over current detection. SWN 12 Lower supply rail for the GH high-side gate driver. Connect this pin to the switching node as close as possible to pins 23- 27. Do not connect this pin to pins 14 – 16. Ground connection for the synchronous rectifier. VINP 13, 29 LX 14-16, 23-27 BST 17 High side driver supply pin. Connect BST to the external boost diode and capacitor as shown in the Typical Application Circuit on page 1. The high side driver is connected between BST pin and SWN pin. VIN 18 VIN connection for internal LDO and PWM Controller. UVIN 21 UVLO input for VIN voltage. Connect a resistor divider between V IN and UVIN to set minimum operating voltage. Use resistor values below 20kΩ to override internal resistor divider. VCC 22 Output of internal regulator. May be externally biased if VIN < 5V. Input connection to the high side N-channel MOSFET. Connect an inductor between this pin and V OUT. ORDERING INFORMATION Part Number SP7662ER-L SP7662ER-L/TR SP7662EB Junction Temperature Range Marking SP7662ER YYWWL X SP7662ER YYWWL -40°C≤TJ≤+125°C X SP7662 Evaluation Board -40°C≤TJ≤+125°C Package Packing Quantity 26-pin DFN Bulk Lead Free 26-pin DFN 3K/Tape & Reel Lead Free Note 1 Note 2 “YY” = Year – “WW” = Work Week – “X” = Lot Number © 2012 Exar Corporation 5/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator TYPICAL PERFORMANCE CHARACTERISTICS All data taken at TJ = 25°C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. Fig. 4: Output Ripple, No Load Fig. 5: Output Ripple, IOUT=12A Fig. 6: Startup Response, No Load Fig. 7: Startup Response, IOUT=6A Fig. 8: Startup Response, IOUT=12A Fig. 9: Load Step Response, IOUT=6A-12A © 2012 Exar Corporation 6/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator Fig. 10: Load Step Response, IOUT=0A-12A Fig. 11: Output Short Circuit Fig. 12: OCP Hiccup Response Fig. 13: VOUT versus Load Current, V IN=12V Fig. 14: Efficiency versus IOUT, VIN=22V Fig. 15: Efficiency versus IOUT, VIN=12V © 2012 Exar Corporation 7/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator Fig. 16: Efficiency versus IOUT, VIN=3.3V © 2012 Exar Corporation Fig. 17: Efficiency versus IOUT, VIN=5V 8/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator THEORY OF OPERATION SOFT START “Soft Start” is achieved when a power converter ramps up the output voltage while controlling the magnitude of the input supply source current. In a modern step down converter, ramping up the positive terminal of the error amplifier controls soft start. As a result, excess source current can be defined as the current required to charge the output capacitor. GENERAL OVERVIEW The SP7662 is a fixed frequency, voltage mode, synchronous PWM regulator optimized for high efficiency. The part has been specifically designed for single supply operation from a 5V to 22V input. The heart of the SP7662 is a wide bandwidth transconductance amplifier designed to accommodate Type II and Type III compensation schemes. A precision 0.8V reference, present on the positive terminal of the error amplifier, permits the programming of the output voltage down to 0.8V via the VFB pin. The output of the error amplifier, COMP, is compared to a 1.1V peak-to-peak ramp, which is responsible for trailing edge PWM control. This voltage ramp and PWM control logic are governed by the internal oscillator that accurately sets the PWM frequency to 300kHz. The SP7662 provides the user with the option to program the soft start rate by tying a capacitor from the SS pin to GND. The selection of this capacitor is based on the 10μA pull up current present at the SS pin and the 0.8V reference voltage. Therefore, the excess source can be redefined as: The SP7662 contains two unique control features that are very powerful in distributed applications. First, non-synchronous driver control is enabled during startup, to prohibit the low side switch from pulling down the output until the high side switch has attempted to turn on. Second, a 100% duty cycle timeout ensures that the low side switch is periodically enhanced during extended periods at 100% duty cycle. This guarantees the synchronized refreshing of the BST capacitor during very large duty ratios. UNDER VOLTAGE LOCK OUT (UVLO) The SP7662 has two separate UVLO comparators to monitor the bias (Vcc) and Input (VIN) voltages independently. The Vcc UVLO is internally set to 4.25V. The Vin UVLO is programmable through UVIN pin. When UVIN pin is greater than 2.5V the SP7662 is permitted to start up pending the removal of all other faults. A pair of internal resistors is connected to UVIN as shown in Figure 15. The SP7662 also contains a number of valuable protection features. Programmable VIN UVLO allows the user to set the exact value at which the conversion voltage can safely begin down-conversion, and an internal VCC UVLO which ensures that the controller itself has enough voltage to properly operate. Other protection features include thermal shutdown and short-circuit detection. In the event that either a thermal, short-circuit, or UVLO fault is detected, the SP7662 is forced into an idle state where the output drivers are held off for a finite period before a restart is attempted. © 2012 Exar Corporation Fig. 18: Internal and External Bias of UVIN Therefore without external biasing the V IN start threshold is 9.5V. A small capacitor may be required between UVIN and GND to filter out noise. For applications with VIN of 5V or 3.3V, connect UVIN directly to V IN. To program the VIN start threshold, use a pair of external 9/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator resistors as shown. If external resistors are an order of magnitude smaller than internal resistors, then the VIN start threshold is given by: For example, if it is required to have a V IN start threshold of 7V, then let R7 = 5kΩ and using the VIN start threshold equation we get R6 = 9.09kΩ. THERMAL AND SHORT-CIRCUIT PROTECTION Fig. 19: Over Current Detection Circuit Because the SP7662 is designed to drive large output current, there is a chance that the power converter will become too hot. Therefore, an internal thermal shutdown (145°C) has been included to prevent the IC from malfunctioning at extreme temperatures. Inputs to an over-current detection comparator, set to trigger at 60mV nominal, are connected to the inductor as shown. Since the average voltage sensed by the comparator is equal to the product of inductor current and inductor DC resistance (DCR), then: A short-circuit detection comparator has also been included in the SP7662 to protect against an accidental short at the output of the power converter. This comparator constantly monitors the positive and negative terminals of the error amplifier, and if the VFB pin falls more than 250mV (typical) below the positive reference, a short-circuit fault is set. Because the SS pin overrides the internal 0.8V reference during soft start, the SP7662 is capable of detecting short-circuit faults throughout the duration of soft start as well as in regular operation. Solving this equation for the specific inductor in circuit 1, IMAX=14.6A. When IMAX is reached, a 220ms time-out is initiated, during which top and bottom drivers are turned off. Following the time-out, a restart is attempted. If the fault condition persists, then the time-out is repeated (referred to as hiccup). Increasing the Current Limit If it is desired to set IMAX > (60mV/DCR) (in this case larger than 14.6A), then a resistor R9 should be added as shown in Figure 18. R9 forms a resistor divider and reduces the voltage seen by the comparator. OVER-CURRENT PROTECTION The Over-current protection feature can only be used on output voltages ≤ 3.3 volts. It is limited by the common mode rating of the opamp used to sense the voltage across the inductor. Over-current is detected by monitoring a differential voltage across the output inductor as shown in the Figure 16. Since Solving for R9 we get: As an example: if desired IMAX is 17A, then R9 = 63.4kΩ. © 2012 Exar Corporation 10/19 Rev. 2.1.0 SP7662 PowerbloxTM 12A 300KHz Synchronous Step Down Regulator into an idle state where the SS and COMP pins are pulled low and both switches are held off. In the event of UVLO fault, the SP7662 remains in this idle state until the UVLO fault is removed. Upon the detection of a thermal or short-circuit fault, an internal 200ms timer is activated. In the event of a short-circuit fault, a restart is attempted immediately after the 120ms timeout expires. Whereas, when a thermal fault is detected the 200ms delay continuously recycles and a restart cannot be attempted until the thermal fault is removed and the timer expires. Fig. 20: Over Current Detection Circuit for IMAX>60mV/DCR Decreasing the Current Limit ERROR AMPLIFIER AND VOLTAGE LOOP If it is required to set IMAX